1. Field of the Invention
The present invention relates to an image processing apparatus, as well as to an image processing method, which performs correction of image magnification in an image handling apparatus such as an image reader which reads an image of an original document, a printer which records an image, a copying machine which copies an image of an original document, and so forth.
2. Description of the Related Art
FIG. 9 shows the construction of a known copying machine, in particular constructions of a reader section 920 and a printer section 921 of the copying machine. Original document sheets stacked on an original document feeder 901 are fed one by one onto a glass plate 902 of an original table, in response to a reading demand generated in the reader section 920 for reading the images on original document sheets. When a sheet of the original document is placed at the right position on the glass plate 902, a lamp 903 of a scanner unit 904 is lit, and the scanner unit 902 starts to move in synchronization with supply of a reading signal to a CCD image sensor 909, thereby illuminating the image on the original document sheet.
The light reflected by the original image impinges upon the CCD image sensor 909 via mirrors 905, 906 and 907 and a lens 908. The CCD image sensor 909 has arrayed thousands of photoelectric conversion cells which constitute pixels, and the light signals thus received by the CCD image sensor are converted into electrical signals on a pixel basis (i.e., each pixel produces its own signal). The electrical image signals thus obtained are subjected to an image processing operation and signals obtained through the image processing operation are sent to the printer section 921.
The image signals delivered to the printer section 921 are converted by an exposure control unit 910 into modulated light signals (a laser beam of modulated intensity in FIG. 9) which irradiate a photosensitive member 911 which has been electrostatically charged, thereby forming an electrostatic latent image on the photosensitive member 911. Then, the latent image is developed as the surface of the photosensitive member 911 moves through a developing unit 912. A transfer sheet is fed from a transfer sheet stacker 913 or 914 in timing with the movement of the leading end of the developed image, and when both the developed image and the transfer sheet pass a transfer unit 915, the developed image is transferred to the transfer sheet.
The transferred image is then fixed to the transfer sheet as the latter moves through a fixing unit 916, and the sheet carrying the image fixed thereon is ejected from the machine by means of a sheet ejecting unit 917. The transfer sheets thus ejected successively are distributed to different bins of a sorter (when a sorting function is used). If such a function is not available or not used, the transfer sheets having the fixed images are stacked on a tray or on an uppermost or a selected bin of the sorter.
A copying machine of the kind described has an enlarging/reducing function, i.e., a function for varying the size of the copy image with respect to the size of the original image. A change of magnification in the direction of main scanning is achieved through an electrical image processing effected on the signals input through the CCD image sensor 909, while a change of magnification in the direction of sub-scanning is achieved by varying the ratio between the peripheral velocity of the surface of the photosensitive member in the form of a drum and the velocity of movement of the scanner unit 904, typically by varying the moving velocity of the scanner unit 904, whereby a copy image of a desired magnification is obtained.
The described arrangement suffers from a problem in that the image reading position is progressively changed in accordance with the movement of the scanner unit 904, so as to undesirably change the image reading magnification, when any deviation of the optical axis occurs in the optical unit including the scanner unit 904 and the CCD image sensor 909 and the optical elements disposed therebetween.
FIGS. 10 and 11 illustrate the manner in which a shift of the optical axis occurs due to movement of the optical system during scanning of the original document image.
In these Figures, a unit 1 is a scanner unit which actually scans the original document image, while a unit 2 is a unit which functions to maintain a constant length of optical path between the point on the original document which is being scanned and the CCD image sensor 909. Any deviation of the mounting angle of a mirror B attached to the unit 2 from the correct angle causes the distance between the unit 1 and the unit 2 to increase in accordance with the movement of the unit 1 in the direction of the arrow away from the scanning start position, resulting in a shift of the optical axis.
The shift of the optical axis causes the inputted image to be contracted when the direction of the shift is the same as the direction of the scanning movement of the scanner unit, whereas, when the shift of the optical axis occurs in the direction opposite to the direction of movement of the scanner unit, the result is that the inputted image is enlarged. A further increase in the deviation of the optical axis causes the path of light leading back from the CCD image sensor 909 to fall out of the area of the optical mirror A, so that the original image cannot be received by the CCD image sensor 909. Consequently, no effective image signal is delivered by the CCD image sensor 909 which serves as the image reading sensor.
Hitherto, it has been necessary to adjust, with high degrees of precision, the positions of the mirrors 905, 906 and 907, as well as the position of the lens 908, in order to minimize the undesirable change in magnitude attributable to a shift of the optical axis.
Replacement of one or more of these optical elements due to, for example, damage of such elements inevitably necessitates not only fine adjustment of the replaced elements but also fine readjustment of other elements. Service engineers are therefore obliged always to carry tools and jigs which are necessary for such fine adjustment. Alternatively, the whole copy machine has to be sent to a service station where skilled engineers and tools/jigs are available, and is sent back to and reinstalled in the user's office after completion of adjustment at such a service station. This heavily burdens personnel involved in service and maintenance, and causes inconvenience to the users.
In order to overcome these problems, a method employing a non-volatile memory means such as a battery-backed-up memory has been proposed as an alternative to the conventional method employing fine readjustment of positions of optical elements such as mirrors and lens. More specifically, according to the alternative method, magnification correction values which have been obtained beforehand are stored in the non-volatile memory means and, when an original document image is scanned by a scanner at a designated magnification, the velocity of the scanner is controlled taking into account the correction value read from the memory means, whereby a correction of magnification of the read image is performed. This correction is carried out to compensate not only for error or change in the magnification taking place in the scanner system but also for error or change in magnification occurring in the printer system. In other words, correction for the scanner system and correction for the printer system are performed in a consolidated manner.
Current development in digital technology has brought about copying machines of the type in which a scanner section and a printer section are operable independently of each other. In order to effect the above-described correction in this type of copying machines, it is necessary to determine the magnification correction values for the scanner section and the printer section, respectively, and to store them in non-volatile memory means. Consequently, it is necessary to prepare and use tools and jigs for determining the magnification correction values for the scanner section and for the printer section, separately, which makes the work further complicated.